Professor Zaehner’s new book is most timely, and—to anybody with any interest in the subject, from whatever point of view—quite absorbing. It is also a pioneer work, for although the study of ‘comparative mysticism’ is not totally new, the little that has hitherto been written about it has been mainly from an a priori standpoint with little regard for the actual records. Moreover, such writing has often been based on assumptions, or wishful thinkings, of very doubtful validity. At one extreme is the assumption that all ‘mystical experiences’ are essentially identical, whether they be of Christians, Moslems, Hindus, Buddhists, Wordsworthian Romantics, drug-takers or schizophrenics. At the other, that only Catholics (or Hindus, or Moslems, or the clinically sane, etc.) have authentic mystical experiences, and that all the rest are frauds, delusions, or at best purely natural phenomena from which any intervention of God’s grace must at all costs be excluded. The outstanding merit of Professor Zaehner’s book is its rigorous empiricism, its careful scrutiny and comparison of the plain facts, which can only be the testimonies of the mystics themselves, or those who have been called such. Even as a collection of texts, and apart from his own thoughtful comments, hypotheses and deductions, this is a most valuable book.